1. Field of the Invention
The invention relates to a fuel cell system and a control method for the fuel cell system.
2. Description of the Related Art
A fuel cell is generally a device that obtains electric energy by using hydrogen and oxygen as fuel. Since fuel cells have excellent environmental friendliness and can realize a high energy efficiency, they have been actively developed as energy supply systems of the future. In particular, among various types of fuel cells, solid polymer fuel cells have good start ability because they are actuated at a comparatively low temperature. Accordingly, solid polymer fuel cells have been intensively researched for applications in a variety of field.
Fuel gas used for power generation in a fuel cell is generated by a reformer or the like. For example, Japanese Patent Application Publication No. 2005-145748 (JP-A-2005-145748) describes providing hydrogen-containing gas obtained by thermal decomposition of ammonia to a fuel cell as a fuel gas.
However, proton conductivity of a solid polymer electrolyte membrane of a fuel cell decreases with the decrease in moisture content. Therefore, the solid polymer electrolyte membrane should include an appropriate amount of water. In JP-A-2005-145748, no water is contained in the fuel gas because no water is generated by thermal decomposition of ammonia in the reformer. Therefore, with the fuel gas obtained by thermal decomposition of ammonia, the solid polymer electrolyte membrane is not humidified. In this case, power generation efficiency can decrease.